Ghrelin is a 28-amino acid peptide hormone synthesized predominantly in stomach and hypothalamus.Recent evidence showed that Ghrelin/GHSR1 a signaling has important roles in divergent neuronal functions,including learning and memory.Our recent results showed that local infusion of picogram of ghrelin blocks memory formation in both rat and mice, which was opposite to the previous reports.The inhibitory effect of ghrelin on memory acquisition were consistently obtained in both basolateral amygdala (BLA) and the CA1 region of dorsal hippocampus.